1. Field of the Invention
The present invention relates to a method of driving a backlight of a liquid crystal display device, backlight driving device, and liquid crystal display device and more particularly to the method of driving the backlight of the liquid crystal display device being effective, when the backlight is divided into a plurality of light-emitting regions to illuminate a liquid crystal panel, in reducing an influence by light leaked from other light-emitting regions to one light-emitting region, the backlight driving device using the method, and the liquid crystal display device capable of reducing the influence by the light leakage.
2. Description of the Related Art
Conventionally, in an image display device of a television set or a like, a CRT (Cathode Ray Tube) is used. Owing to technological development thereafter, in recent years, various types of display devices are employed. These display devices include a liquid crystal display device. In the liquid crystal display, its liquid crystal panel itself is non-luminous and, therefore, a backlight is placed as a light source on a rear side of the liquid crystal panel and, by controlling transmittance of the liquid crystal panel according to an image signal, an image is displayed on a display surface.
The backlight employed in the liquid crystal display device is ordinarily used in its lighted state. As a result, if the whole display area is divided into a plurality of display regions and there is a given display region where black is to be displayed on a display surface of the liquid crystal panel, the given display region is made the brighter due to light leaked from other display regions surrounding the given display region. This is unlike a case where black is displayed by the CRT or a like which light emission is directly controlled. As a means to resolve the disadvantage, a method is available where luminance of a backlight is controlled according to an image signal to improve contrast (Non-patent References 1 [SID (the Society for Information Display) 04 DIGEST p 1548] and 2 [SID 05 DIGEST p 1380]).
An example is disclosed in Patent Reference 1 (Japanese Patent Application Laid-open No. 2005-258404). A liquid crystal display device disclosed in the Patent Reference 1 is so configured that, when an image based on an input image signal is displayed on a display surface of a liquid crystal panel while the liquid crystal panel is being illustrated by a backlight from a rear side of the liquid crystal panel, display data for every color to be applied to the liquid crystal panel and an amount of light emission of every color of the backlight are simultaneously controlled according to an image signal for every color of an input image signal and an output signal from an optical sensor which detects light emission from the backlight. Then, a controller used to exert control of the above performs a conversion of a gray level of an image to be displayed on the liquid crystal panel and luminance of the backlight. Therefore, the liquid crystal display device performs dynamic contrast control configured to change luminance of the backlight according to an image signal to be displayed on the liquid crystal panel. To exert the dynamic contrast control, an LED (Light Emitting Diode) of Red, Green, and Blue is used as the backlight, which serves to widen a chromaticity region and to increase modulation of a color (color hue) in an image memory.
Moreover, according to the disclosure in the Patent Reference 2 (Japanese Patent Application Laid-open No. 2007-052105), the backlight of the liquid crystal display device is divided into a plurality of light-emitting regions and an optical sensor is placed in every light-emitting region. This optical sensor measures light emission from the backlight for every light having passed through a color filter and controls, based on the measurement result, the light emission intensity of an LED making up the backlight in every light-emitting region and in every light-emission color.
However, in the configurations described in the above Patent Reference 1, the dynamic contrast control is exercised on the entire liquid crystal panel. Therefore, the related technology has a problem in that, when an image is to be displayed on the liquid crystal panel according to an image signal, if it is desired that an LED having high luminance and another LED having low luminance serving as the backlight exist in a mixed manner, light from the LED having high luminance leaks into a region corresponding to the LED whose luminance is required to be lowered and, as a result, it is impossible to fully lower the luminance of the light-emitting region corresponding to the LED whose luminance is required to be lowered.
Therefore, it is desirous that a backlight has a structure in which no light leakage occurs. However, by simply applying the division of light-emitting regions disclosed in the Patent Reference 2 as a method of reducing the light leakage, the complete elimination of the light leakage to the light-emitting region from other adjacently-placed light-emitting regions is difficult. Also, since the light emission intensity of an LED changes depending on a change in temperatures, it is difficult to avoid a change in color hue occurring while the dynamic contrast control is exerted.